ffmpeg-skill

What the source does

• FilesystemDeclared5 observations
• NetworkNone observedNo outbound calls in the source
• ShellDeclared1 observation
• DependenciesPinnedNothing floats
• SecretsNone foundNo keys in source

Five audit layers

Gates applied: no behavioural pass.

- **A ZWJ no longer starts an emoji cluster.** U+200D ZWJ and U+200C ZWNJ are ordinary Indic/Persian orthography, so `क्ष` (ka + virama + ZWJ + ssa) was detected as the emoji cluster `94d-200d`: a Hin

U+200D ZWJ and U+200C ZWNJ are ordinary Indic/Persian orthography (`क्ष` is

module = importlib.import_module(module_name)

module = importlib.import_module(module_name)

h = hashlib.sha1()

return hashlib.sha1((json.dumps(recipe, sort_keys=True) + "\0" + project_content).encode()).hexdigest()[:12]

return hashlib.sha1(json.dumps(payload, sort_keys=True, ensure_ascii=False).encode()).hexdigest()

for step in ([str(evil)], ["../../../../tmp/does_not_matter.py"]):

raw += bytes.fromhex(rest.strip().split("  ")[0].replace(" ", ""))

assets/demo.gif

Audit 0.4.1 · source sha ac177ce07ae4 · 23 Oct 2026Report an issue or request a re-scan

• Publisherkajisho5 GitHub userOwner of the repository this skill is read from
• Source folderkajisho5/ffmpeg-skillThe exact folder we audited
• LicenceMITAs the repository states it
• Commit pinned for this verdictac177ce07ae4A new audit runs when the source changes
• Repository statusNot archivedPushed today
• Sandboxed runNot runSkills are read, not executed; layer L4 is skipped

Its description: Edit video and audio with local FFmpeg from natural-language requests: cut, trim, join, resize/reframe (9:16, 1:1), speed change, captions and subtitles (SRT/ASS, animated, karaoke), logos and text overlays,…

---
name: ffmpeg-skill
description: 'Edit video and audio with local FFmpeg from natural-language requests: cut, trim, join, resize/reframe (9:16, 1:1), speed change, captions and subtitles (SRT/ASS, animated, karaoke), logos and text overlays, lower-thirds and titles, silence removal, multicam and external-mic sync, loudness normalisation, HDR/Dolby Vision to SDR, LUTs, background music with ducking, platform exports (YouTube, Reels, TikTok, X), compliance checks, scene detection and highlight reels, contact sheets to inspect results, and whole-edit project files. Use this skill whenever the user mentions a video or audio file (mp4, mov, mkv, wav, m4a), footage, a clip, captions, subtitles, a reel or short, YouTube/Instagram/TikTok delivery, LUFS, sync, transcoding, ffmpeg, or asks to make something "60 seconds", "vertical", "louder", "captioned" — even when they do not say "edit". Python 3.10+ standard library only (3.9 deprecated), no cloud, no API keys.'
---

# ffmpeg-skill

Scripts live in `scripts/` next to this file; run them with `python3 <skill-dir>/scripts/<name>.py`, and delivery templates in `templates/`. This file is enough to do a job: the table below routes the request, and `--help` on the script about to run is the cheapest full flag list. A reference file costs as much as this one; open one only for a question you have: `references/scripts.md` (every flag of all 42 scripts), `references/devices.md` (iPhone HDR, GoPro, DJI, screen recordings, Zoom), `references/gotchas.md` (the long form of the one-line rules at the end). MCP: `tools/list` shows only the core 12 by default; the other 30 (per this table) stay callable by name via `tools/call`, described by `contract --json`; set `FFMPEG_SKILL_MCP_FULL=1` for all 42.

Shared flags (every script): `--dry-run`; `--json` (output path, its probe, the commands run); `--json-brief` (status/output/verified + a `summary`; prefer on writing steps); `--fast` (preview quality); `--progress` (percent/ETA); `--timeout SECONDS` (`kind: timeout`, default 1800); `--overwrite` (step 7); `--plan FILE` (a dry run `render.py FILE` runs later; refuses if an input changed). Re-encoding tools also take `--hw` (Apple Silicon GPU, big files; `FFMPEG_SKILL_HW=1` = default, not export), `--codec h264|hevc|av1|prores` and `--quality N`: unset, SDR is x264 (`cut.py --keep-hevc`: HEVC source stays HEVC), HDR is x265 Main10; `prores` needs `-o NAME.mov`, `h264` refuses HDR (`color.py --to-sdr` first).

Writing tools run nothing under `--dry-run`; the measuring tools (`probe`, `check`, `sync`, `multicam`, `scenes`, `cropdetect`, `report`, `silence`, `loudness`, `stabilize`; `overlay` for a multi-line `--text` on FFmpeg 8.0-8.1.0) may still run ffmpeg/ffprobe, skipping artifacts/side files (`--edl`, `--sheet`, a generated `.ass`); `verify` ignores the flag. Per tool: `contract --json` `dry_run`.

## Workflow (in this order)

0. **Environment, only on failure.** Never start a job with `doctor`: a broken machine fails with `kind: missing_tool` or an ffmpeg error naming the filter/encoder. Run `python3 <skill-dir>/scripts/_contract.py doctor` (or `npx ffmpeg-skill doctor`) after such a failure, or when asked what the machine can do: read `ok`/`usable`, report the missing capability. `contract --json`'s tool schema is for a *planning* agent, not this workflow.
1. **Probe what you must plan from.** Run `probe.py` on each input you plan from — duration, fps, resolution, codecs, channels, `variable_frame_rate_suspected` — and whenever the user asks about a file. No separate probe before every edit: every writing tool's `--json` already carries its input and a probe of the output. Plan from real numbers, never assumptions.
2. **Prefer lossless.** If the request can be met without re-encoding (plain cuts on keyframes, remuxing, audio-only changes), do not re-encode. `cut.py` and `loudness.py` stream-copy video by default; `--accurate` on `cut.py` only for frame-exact cuts.
3. **Plan with `--dry-run --json`, then execute.** Trust `--json`, not a dry run's summary line, for any number in the plan (a dimension there can be a placeholder). Use before long encodes, to report facts. Never point `-o` at a file you did not create in this job unless the user asked for it to be replaced; pass `--overwrite` only then.
4. **Chain in a sensible order.** A delivery request with no other editing is one template run (`render.py --template NAME INPUT`), not a hand-built chain. Otherwise: colour (HDR→SDR / LUT) → cut → join → silence → fit → caption/overlay → sync → audio → loudness → export. Frame changes before captions, so text is sized for the final frame. Re-encode as few times as possible: intermediates at CRF 18, `export.py` last. **Three or more steps: `render.py` with a project.json.**
5. **Check the deliverable.** Before reporting, run `check.py OUTPUT --platform X` for the destination named (a template run already does). Format rows (codec, pixel format, size, true peak, colour tags, VFR) are safe to fix. Judgement rows change content: duration (cut loses material), aspect (crop loses edges), fps (drops motion), loudness (ambience must not be boosted) — fix only when the request implies the answer, else state the choice and its cost. Mention WARNs; do not chase them.
6. **Verify the output.** Confirm duration, resolution, fps and audio match the request, from the writing tool's `--json`/`--json-brief` probe or `probe.py`, and report those numbers ("final.mp4: 59.98 s, 1080x1920, 30 fps, AAC stereo"). A step is done only when the script exited 0 and the output probes as expected: a non-zero exit, a missing or empty file, or a probe that contradicts the request is a failure reported with the script's error message.
7. **Keep the user's originals.** Never overwrite the source; write new files next to input or where asked. An existing output path is refused (`kind: input`); `--overwrite` is the one way to say "yes, replace it".
8. **Look at the picture.** Whenever the picture

Excerpt, first 6,000 characters of SKILL.md, verbatim from the audited commit. It is text from someone else’s repository, quoted so you can judge it before your agent reads it.

1. 2026-10-23
   ✕BLOCK D 69 / 100

   first audit · source ac177ce07ae4

Questions about ffmpeg-skill

• github.com/kajisho5/ffmpeg-skill — the audited source at commit ac177ce07ae4 and every finding aboveObserved · 23 Oct 2026

Spotted something wrong? Report a correction · Methodology